Telephone system



April 3, 1928., 6

. H. D. cURRxER ET A1.

TELEPHONE SYSTEM 3 Sheets-$heet 1 April 3, 1928. 1,664,665

H. D. CURRIER E1' AL.

TELEPHONE SYSTEM $5V Sheets-Sheet 2 Original Filed Sent. @41920:

pc f /9/ 192 April 3, 192s.,

H, D. gunmen ET m. TELEHONE SYSTEM 5 Smets-Sheet 3 Patented Apr. 3,1928.

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y 1,664,655 carena OFFICE..

HIRAM D. CURRIER AND WILLIAM G. SKULL, 0F CHICAGO, ILLINOIS,v ASSIGNORSTO i KELLOGG- SW'ITCHBOARD AND SUPPLY COMPANY, OF'CI-IICAGO, ILLINOIS, ACOR- PORATION 0F ILLINOIS.

TELEPHONE SYSTEM.

Original application filed September 18, 1920, Serial No. 411,289.Divided and this application filed March 9, 1925.

Our invention relates to telephone systems and has to do moreparticularly with trunk circuits for use with private branch exchangesystems in which the trunk circuits are used between local privatebranch exchange substations and manual exchanges or automatic exchanges.

A feature oi our invention is the provision of means whereby the privatebranch exchange operator may, by the use of a calling device, dial fromher position and actuate the apparatus at the automatic exchange toselect the wanted called line without thev plug of the trunk circuitbeing in a local f line jack.

Another feature of our invention is that the operator may actuate thecentral office exchange switches with the plug of the trunk inserted ina local subscribers line jack, either when the local subscriber has hisreceiver on or ofi the switchhook.

A further feature of our invention is the provision of means whereby theinstant the private branch exchange subscriber replaces his receiveruponthe switchhoolr, means are actuated in the trunk circuit to clearthe line through to the main exchange, so that,

should the private branch subscriber again remove his receiver beforethe trunk plug is removed from the local jack, the trunk will `again beseized and extend the connection through to the main exchange, and inthe event that the private branch exchange substation is equipped with acalling device, the

subscriber may again actuate the automaticV apparatus to seize anothercalled line as wanted. In the event that the trunk circuit was used toextend a connection to a main manual exchange, when the private branchexchange subscriber removes his receiver the trunk is again extended tothe said main exchange and the main exchange operator signaled.

Another feature ot our invention is the provision of means so that afterthe private branch exchange subscriber hangs up and clears the trunk tothe main exchange, should :mother call be extended from the mainexchange to the branch exchange beforethe plug is taken down. the calllamp of the trunk circuit will be operated, but not the bell otl theprivate branch exchange subfscriber. f

Serial No. 13,983.

The above features, as well as others of our invention, will be moreparticularly pointed out in the ensuing specification and appendedclaims.

This application is af divisional application of our applicationL111,289, filed September 18, 1920, and issued April 7, 1925, as U. S.Patent No. 1,532,652.

For a better understanding of our invention, reference may be had to theaccompanying drawings, in which Fig. 1 illustrates one embodiment of ourinvention as applied thereto;

Fig.V 2 illustrates another embodiment of our invention; and

Fig. 3 illustrates an automatic exchange system adapted to operate inconnection with vour invention.

Referring now more in general to our invention as illustrated in Fig. 1,we show a calling substation A terminating at the main exchange M in aline circuit B, comprising the usual line relay LR, cut-off relay GO,line signal L and the multiple jacks J.

The` cord circuit C located at the main exchange M is shown for use inextending connections from the line circuit B and comprises an answeringplug AP and a. calling plug Cllthe two plugs AP and CP being connectedby the heavily marked conductors, the said conductors having thecondensers K Vand K interposed therein. Associated with the answeringend ofthe cord circuit C is the answering tip supervisory relay AT andan answering sleeve supervisory krela-y AS, the two relays controllingthe answering supervisory lamp AL. Associated with the calling end ofthe cord circuit C is a calling tip supervisory relay CT and a callingsleeve supervisory relay CS, the two relays contr-olling the callingrsupervisory lamp v operators position, andwvliich are terminals Voftrunkcircuits PC. The trunk circuits PC extend to a private branch exchangeSwitch- Y board 53B, and the said jacks'llJV areV con- Lnected .to thesaidl trunk circuits PC, which terminate at the private branch exchangePB over the heavilyinarked conductorsl 32 and 42.

l Thepriva-te branch exchange trunk PC ,is

provided with a kring-up vrelay RU, ivhich l `:reilen/fH-'Jeijates*whenringing current isgappliedV troni adistant exchange. VThe ring-up frelay Ruppert energizatioii, brings about thelightingfof .the line lainpLL, to notify A, the .operator at the-private. branch exchange that" acallv awaits her. attention. A

'.,list-enignglkeyLl is provided which, vwhen actuated,connectstheoperators set O to l the. trunlconductors for the usualpurposes.

A V,conibiified `disconnect and guard relay VDS is Valso providedv,which 1S energized uponl the Iactuation of the listening key LK to .pnal when the operator answers the-call. A sleeve relay SL is'also`provided,`ivhich bring about the eiiacenient ofthe line sig- ;telay isenergized when ,the operator inserts the trunlrplug ,TPinto the localline .'jack J ofi the Wanted station at the private ,brancllrexchange Aringing key RK is also, providedgwhich when. actuated, con-U y `nectsringing generator G tol signal the labout the effacement of the holdinglampl 40 IHL `disconnects the holding` coil.

calledffor station 4at ,the private branch er:-

change `.Asnpervisory relay 'SR is also provided `which is energizedwhen the party at. thecalled private branch exchange substation answers.A holding relay 49 is also provided, which energizes upon theenergization` oi the 'supervisery relay SR to bring acros'sthetrunl;conductors, the said, holding coil `being -,bridged across `Vthetrunlnconductors upon, the energization of the. relay DS. Adisconnectsignal DSL-is also-.provided for tlieusiial disconnectsignaling purposes. vAn, operators disconnect -relay`-92r and a trunk`cut-off relay CORY are providedand are brought intooperation inYconnection with the .trunk -circuit 13C-When 50 M the: privatebranchexchange ,operator O is .,eztendingya connection :troni the-localpriyate branch exchangesubstation to an autoaut'oinatic exchange.

irnatic `nain exchange. A calling ldevice. GD isalso provided `Whichisused' by the oper- Kater in .extending a connection toa nia-in Aalso`pfioyided for the-usual purposes..r To

` trunllg PC We show aflocal ,private branch @schaarse .siibstetienflterminating there# Y in the; tack JT', line. relay. LEZ and 'a line]ktiti the right of the private branch'eiichange signall/v.l A Y i "2vvehillustrate a modified forni of V trunk-circuit Vin yvhich,A upon4the energization oa rela of the trunk circuit PC after IA, night -jackNJ isV the Vbranch exchangesubscriber replaces his receiver and Wishesto recall, the removal of the receiver brings about'the lighting of thevline lanip to notify the `operator that the localsubscriber Wishes torecall. The trunk circuit PC is provided with apparatus siniilar tolthat mentioned in connection With the trunk circuit PC oflilig. l.

Having described in general the apparatus Which embodies our invention,We Will now describe nioreuin detail. the operation ofthe systein vasillustrated.

Assuming ,now that the subscriber at the substation A at the .inainexchange initiates Aa, call, the removal of the receiver at thesubstation closes an energizing. circ-uit for line` relay LR' of thesubscribers associated line circuit B, and thesaid relay LR', uponenergization7 closesl its alternate contact, esta-blishing a circuitthrough the line lainp L, `which larnpLis now lighted. The operator plug.AP and, jack J 'to ground Vthrough theV Winding-of the cut-ofi' relayC0. `Therelay C() iiirionenergization opens the energizinglv circuit oftheline relay LR, which relay LR now restores and'effaces the linesignal L. flhe answering tip supervisory relay AT Y also energized overthe line to prevent the premature lighting` of. the `anrnveringsupervisoiylainpfAL. The operator of the cord circuit C now actuatesherV listening key LK .to connect lier operators set Oto the cordconductors and inquires thc Wants ot the calling subscriber at thesubstation A.

Assuming that it is the subscriber Flocated at the private branchexchange PB .that is desired, the `operator now inserts the calling plugCP ,into a trunk jack TJ leadingto the private branch exchange P B atwhich the subscriber F is located. The insertionrof the. said plug CPinto the jack TJ establishesan energizing circuit for the 'callingsleeve supervisory relay CS, and the cut-offA relay CO', troni batterythrough the windiiigof the relay CS, norinal Contact of theifinging keyRK, sleeve contacts of the Vconnected Vplug and trunk jack HIJ,

through the `Winding of the Vrelay CO to ground. `The closingofalternate-contact 30of the ,relay CS closes a circuit for thecalling,supervisory lamp CL frein battery,

through the Winding of the said lampjCL,

alternate contact 30, normal coiitactglv of the calling tip supervisoryrelay CT to ground, the lamp CL remaining-lighted unlise incassa 8 tilthe private branch exchange operator an swers the call, at which timethe calling tip supervisory4 relay CT energizes to ei'i'a'ce thesupervisory signal CL. The operator at the main exchange now operatesthe ringing key RK to connect ringing generator Gr to the trunk circuit.Ringing current is thus ex tended over the trunk conductors, whichcircuit may be traced 'from the ungroundcd pole of the generator G,\tipcontacts ot the connected plug Cl? and trunk jack TJ, trunk conductor32, normal contact 33 of the night ack NJ, normal contact 34 of thedialing relay COR, conductor 35, condenser 36, through the winding otthe ring-up relay RU, conductor 37, normal Contact 3S oit the disconnectrelay DS, conductor 89, normal contact 40 of the dial relay COR, norlnalcontact 4l of the night jack NJ', trunk conductor 42, sleeve contacts otthe connected trunk jack TJ ot' the plug CP to battery and ground at thealternate contact of the ringing key RK.

The closing ot alternate contact 43 ot the relay RU closes an energizingcircuit ot the line lamp LL from battery through the lamp LL, to thegrounded alternate contact 43 et relay RU. The operator noting thelighted line lamp LL now actuates her listening key LK. The closure otalternate contact 44 ot .listening key LK establishes an energizingcircuit for the disconnect relay DS, traced from battery through theupper Winding of the relay DS, conductors 45, 46, alternate contact 44of listening key LK', conductor 47, normal contact 48y of relay 49,conductor 50 to ground at normal contact 5l of the ringing key BK. Theclosing of alternate contact 44 ot key LK establishes a circuit for theholding lamp HL, traced from battery through the said lamp HL, closedcontact 44' ot key LK', conductor 47, normal contact 4S ott relay 49,conductor 50 to.

ground at normal contact 5l ot ringing key RK. It the call proceeds nofurther than the operator, the circuit is cleared by the operator at thebranch exchange actuating the ringing key RK, Which opens the circuit ofrelay DS and allows it to restore to normal. The relay DS uponenergizing unlatches the alternate contact 430i the relay RU, allowingit to restore to el'ace the line signal LL. The relay DS new closes alocking circuit for itself trom battery through. its upper Winding, itsalternate contact 52, conductors 5S and 47, normal Contact 48 ot i relay49, conductor. 50, to ground at normal contact 51 of the ringing key RK.

The closing of alternate contact 38 of the relay DS bridges the holdingcoil HC across A the trunk conductors trom the point 55, over conductor85, through the Winding ot' the holding coil HC, normal contact 56 or'the relay 49, conductor 57, alternate contact 38 of relay DS, conductor39 to the point 58.

lWhen the holding coil HC is thus bridged across the trunk conductors,the relay `GT ot the. cord circuit C at the main exchange operates toopenfits normal contact 3,1, thus opening the circuit ot the callingsuper! visory lamp CL, to thus elace the said lamp CL and notify theoperator at the main exchange that the operator has an@ Assuming that it1s the` lay DS, conductor 61, the sleeve of the plug TP to ground at thesleeve ot the jack J The relay SL upon energization closes its alternatecontacts 62 and 63, thereby closing the trunk conductors through to thecalled substation. The closing of alternate Vcontact 64 of the sleeverelay SL multiplies the ground trom the sleeve ot the jack J to therelay DS, this multiple ground connection to the relay DS being tracedfrom battery through the upper Winding of the relay DS, conductors 45,46and 65, alternate contact 64 ot relay SL, conductor 66normal contact 67ot relay 49, conductorV 6l, through the sleeve of the trunk plug TP toground at the sleeve ot the jack J for purposes as will be presentlydescribed. The ground from the sleeve ot' the jack J also extends to theholding lamp HL, traced jtrom battery through the lamp HL, conductors 46and 65, alternate contact 64 of relay SL,

conductor 66, normal contact 67 ot' relay 49,

conductor 6l, sleeve ot the plug TP to ground at the sleeve ot the jackJ', the said lamp HL remaining lighted until the subscriber F answers;

The operator now actuates the rin-ging key RK to connect generator G tosignal the called-:tor station F, the ringing circuit being traced fromthe ungrounded pole ot the generator Gr, tip contacts of the plug TP andthe jack J', through the condenser and call hell ot the called stationF, the ring contacts ot' the jack J and plug TP, through the alternateContact of the ringing key RK `to battery and ground..

The opening ot normal contact 5l of the ringing key RK opens the lockingcircuit ot the relay DS.` but duc to the tact that the ground :troni thesleeve of the jack J is also n'iultipled through the upper winding` ofthe relay DS, 'as'just described, the relay remains energized during thetime that the ringing key is actuated. The party at the station F, inresponse to hisicall signal, ren'ioves his receiver from thesyvitchhook, bringing about the energization of the supervisory relaySR.The Circuit for relay SR extendsover the called line F.

closing of alternate contact 7 0 of the e supervisory. relay SRestablishes an energizing ,eircuit for the rela-y 49, traced frombattery through the upper Winding of the relay 49, eenduct'or 71,through the lower Winding .ofthe relay DS, conductor 72, alternate con-.ftact 70 of therelay SR, conductor 61,

through the sleeve contact of the trunk plug TP to .ground at the sleeveof the jack JC Y The opening of normal contacts 48 and v6.7 @of therelay.49 opens the locking circuit through the upper Winding of therelay DS, but the series energizing circuit through theuppervvinding ofrelay 49 and the loiver Winding of relayDS permits the continuedenergiziation of the said relay DS. The opening of normal. contact 56 ofthe relay .49 also removes the holding coil HC from kacross the trunkconductors. The closing of alternate contact V67 of `the relay 49 estab-`lishes a locking circuit for relay 49 from battery,@through vtheresistance 75 and the Vjlovver Winding of the relay 49, alternatecontact 67 of the4 relay 49, conductor 6l, through 'the sleeve ofthetrunk plug TP to ground jat the sleeve ofthe jack J. The opening of iynormal contact 67 of relay 49 opens the energizing circuit of lamp HL,which vis novv effaced,"and notifies the operator at the private branchexchange PB that the party at the private branchsubstation Fhasanswered. The subscriber at the main ex-v change andthe par-ty atstation F ofthe L Aprivate branch exchange are now in conversationalcircuiti'V The said talking circuit f may be traced over the heavilymarked conductors Assuming' that the subscriber at substation A and theparty at the private branch exl change station F have finishedconversation,

the restoration of the receiver at the station F ofthe private branchexchange opens the" energizing circuit of the supervisory relay SR, andthe opening of alternate contact i [of the said relay SR interrupts theground Y connection from the sleeve of the jack J',

.and the relay DS thus restores to normal.

v'The relay DS upon de-energization opens its alternatecontact-60,'Which opens the enerj gizing circuit of the sleeveerelay SL,which relay restores. The openingof its alternate contacts 62 and 63interrupts the trunk conductors.y The closing of its normal contacts `76and 77 places the'local private branch exchange battery upon the trunkconductors, extending to the substation.

The closing. of normal contact YOothe sleeve relay SR` novv closes Vanenergizing circuit A for the disconnect signalk DSL,`

i .y traced fro'rnbattery through thelament of contacti78 of the relay49, conductor 79,` l ce normal lcontact'7() of the relay SR, conducthesaid disconnect signal'v DSL, alternate tor 61, through the sleeve ofthe trunk plug TP to ground at the sleeve of the'jack J. Thedisconnectsignal lighting `notifies the private branch exchange operatorfthat thesubscriber has replaced his receiver upon the switchhook.

The relay 49 remaining energized to Iground at the sleeve of the iaclrJ`through .its locking contact 67, prevents the holding main exchangesubstation A replacing hisV receiver, opens the circuit through thevanswering tip supervisory relay AT, which relay [upon lrestorationclosesv a circuit through the answering supervisory lamp AL, which lampAL is lighted toV- notiy the operator that the subscriber atsubs'tationA hasreplaced his receiver.` The operator at the main exchange notingthe` two lighted signals'AL and CL now withdraws they an' swering plugAP and calling plug CP4 from the respective jacks J and TJ to ,openithecircuits ot relays AS and GS of thefcord circuit C, which relays AS andGS upon deenergization eiface the supervisory signals AL and CL. RelaysCO and CO also restore, thus placing the Vapparatus at the main exchangein. condition for use in'establishing other connections. The privatebranch exchange operator at PC, noting the lighted .disconnect signalDSL, withdraws the trunk plug TP fromV the jack J', Which-,opens the.locking circuit of the 'relay 49. The relay 49 upon deenergizationrestores and opens its alternate contact 7 8 to eii'ace the disconnectsignal The private branch exchange trunk circuit PT is now at normal andavailable for use in establishing other connec tions. v

, Assuming now that the subscribers-have replaced their respect-ivereceivers upon their respective sivitchhoolrs and that the partyat theprivate branch exchange substation F 'again removes his receiver beforethe trunk plug TP has been removed from the jack l',

this removal of the receiver brings about the energization ofsupervisoryr relay SR. traced `from battery through normal Contact 77ofV sleeve relay SLV through the `Winding of said relay SR, ringcontacts of the connected plug TP and' jaclrJ throughV the closedcontacts of the substation switclihook,1baclr; through the tip contactsof the connectedfplug TP andjaclr J ,to ground katnormal Contact 7 6 ot'relay SL. Therelay SR upon energiza-` tion closes 'itsalternatecon-tact70, Vestablish'- ingan energizingcircuit for the relayDS,

traced from battery throughl the upper winding ot relay 49, conductor 71through the lower winding otrelay DS, conductor 72, al-

ternate contact 70 ot relay SR, conductor 61, y

nate contact ot relay DS, conductor 61,v

sleeve contact ot' t-h-e plug TP to ground at the sleeve of the jack JThe relay SL upon energization closes its alternate contacts 62 and 63and thus extends the station F at the private branch exchange PB to mainexchange, the main exchange battery thus holding the relay SR energized.The line relay LR at the main exchange will now operate, providing theplug CP has been Withdrawn from kthe jack, over a circuit traced frombattery through the winding ot relay LR, normal contact 80 ot relay CO',conductor 32, normal contacts 33 and 34, alternate con` tact G2 of relaySL, tip contacts ot' the plug TP and jack J, through the closed contactsof the substation F, ring` contacts of the jack J and plug TP, throughthe winding otrelay SR, alternate contact (i3 of relay SL, normalcontacts 40 and 41, conductor 42, to ground at normal contact 81 ofrelay GO. The line relay LR upon energization closes its alternatecontact to light 'the trunk signal TS, whichnotiiies the operator atrthemain exchange that a private branch ex change station is calling. Therelay SR upon energization also opens the circuit ot' the disconnectsignal DSL, which also gives the private branch exchange operator anindication that the party at the station F has called. rlhe closing oi'contact 300 of key LK when the operator, for any reason, actuates thekey LK while the plug TP is in jack J', after the subscribers havereplaced their receivers, operates to shunt out relay 49, therebydeenergizing the same.

Assuming that the subscribers have replaced their receivers and theoperator at the main exchange desires to extend another call to thebranch exchange before the plug TP is taken down, the mainexchange/operator applies ringing current to the trunk circuit andoperates the relay RU as before described, causing the lamp` LL toglow,thus notifying the private branch exchange operator that anothercall is being extended to the branch exchange.` The operator yagainoperates her listening lrey and completes the connection. rPhe ringingcurrent applied to the trunk circuit by the main exchange operator didnot reach the substation F even though the plug TP .was in the jack J,'for the reason that the trunk circuit was open at contacts 62 and G53ot relay SL.

The branch exchange operator may ex-` tend a,- connection to the mainexchange by operating her listening lrey, even though the trunk plug TP1s not 1n a jack.

Assuming now that a call is extended from y an automatic exchahge asillustrated in Fig. 3 to the private branch exchange PB, the ringingcurrent which is applied from the autoc matic exchange extends over thetrunk conductors 32 and 42 and operates the ring-up relay RU ot thebranch exchange trunk PC which was seized by the connector of theautomatic exchange. The relay RU upon energizing closes its alternatecontact 43 to light the lamp LL and the operator at the branch exechange PB in response to the signal actuates her listening key LK. Theactuation of the key LK closes a circuit Jfor relay DS and the allclosing of its alternate contact 38 bridges the Y holding cord HC acrossthe trunk conductors to operate ringing control means at the mainautomatic exchange to disconnect ringing current from the trunk circuit.The operation oi' the trunk circuit PC is the same as that described inconnection with a manual connection as just described.

VVhenthe trunk circuit is used in connection with a main automaticexchange, it may terminate at the main automatic exchange in a lineswitch ot the usual type and in the banks of rotary connectors orstraight line connectors such as is described and illustrated in the U.S. Patent No. 1,194,741, issued August 15, 1916, to Harry H. 1de. Inthis case ther conductors 32 and 42 leading to Vthe main exchange willnot be included in the apparatus, the trunlr circuit being connecteddirectly to the conductors leading to the automatic exchange, and,therefore, the operation of the trunk circuit at the branch exchangewill not atleet the apparatus at the manual main exchange.

The operation of the trunk PC when a private branch station calls a mainexchange subscriber of an automatic exchange, is as follows: Assumingnow that the operator at the private branch exchange PG wishes to extenda connection to a subscriber at an automatic exchange, she actuates herlistening key LK', which closes a circuit for the disconnect relay DS,.traced from battery through the upper winding of the relay DS,conductors 45 and 46, alternate contact 44 of the listening key LK',conductor 47, normal contact 48 ot relay 49, conductor `50 to ground atnormal contact 51 of the ringing lrey RK. The closing of alternateContact 38, upon the energization of DS, bridges the holding coil HCacross the trunk conductors, as previously described, thus operating aswitch to connect the trunk to either a selector switch or a connectorswitch, depending upon the size of the exchange. The operator Emi nowoperates her calling Vdevice .CD to send the required number of impulsesto operate Referring now to Fig. 2, weillustrate a modiied `:form ot ourinvention whereby when the subscriber at the substation F of the privatebranch exchange replaces his receiver, the energizing of a relay bringsabout instantaneous disconnection. When the subscriber of the privatebranch exchange substation F' recalls before the plug TP' is Withdrawnfrom the local jack J 2, hek

is immediately enabled to signal the operator. It is understood that thetrunk PG terminates at the main exchange in equipment similar to thatshown in Fig. 1, in which the trunk PC terminates. Assuming now that thecall is extended to the private branch exchange PB', the ringing currentfrom the main exchange extends over the trunk conductors, throughrnormal contact 150 of the relay COR', conductor 151, through thewinding of said relay RU', normal contact 152 of relay DS', conductor153, normal contact'154 ot relay COR', there back to the main exchange.Relay RU' upon energization closes its alternate contact 155, whichcloses an energizing circuitlor the line lamp LL of the private branchexchange trunk PC', from ground through alternate contact 155 ot relayRU', conductor 156, through the lamp LL to battery.

.The operator at the private branch ex-` change circuit PC noting thelighted line signal LL', now actuates her listening key LK2 to connecther opera-tors set O2 to the trunk conductors. The closing of alternatecontact 157 of the listening key LK2 closes an energizing circuit forthe relay DS', traced from battery through the lower winding of therelay DS', conductor 156,A alternate contact 157 of the listening keyLK2, conductor 159, normal contact 166 of the re,- lay 161, conducto-r162 to ground at normal contact 168 of the ringing key BKZ. The closureof alternate contact 152 of the relay DS' bridges the holding coil HCacross the trunk conductors for purposes as previously described inconnection with Fig. 1. The closing of alternate contact 164 of therelay DSf closes the locking circuit Jfor the relay DS', traced frombattery winding of the said relay DS', alternate contact 164,'normalContact 160 of the relay 161, conductor 162 to ground at normal contact` 163 of the ringing key RK2. The relay DS upon energizationunlatches the con tact 155, which is in its alternate position, allowingthe said contact to restore and efface the line signal LL. The operatorot the private branch exchange PB', having been informed that it is'theparty at the substation F that is wanted, now inserts the trunk plug TPinto the jack J2 ot the local line. Upon the insertion ot the trunk plugTP' into the` jack J2, permanent ground upon the sleeve of the jack J 2now,l ext-ends oiE the relay from lrelay DS', but

through the upper 'lower windingfot the relay DS to battery.

through the lower winding of holds the said relay DS eneris actuated.

This ground the relay DS gized when the ringing key BKZ An energizingcircuit for the holding signal HL is also closed, the circuit being itraced from battery through the holding signal HL', conductor 158,normal contact 166 161, conductor 165, the sleeve ot the trunk plug TP',to ground at the sleeve of the jack J2, the said lamp HL' remaininglighteduntil the subscriber at the local station F' answers. The ringingkey` Rh@ is now actuated to send ringing current to the called localstation F', ringing current being traced from the ungro-unded pole otthe generator G2, alternate contact of the' ringing key Rl?, tipcontacts ot the connected plug TP' and jack J2, through the' condenserand call bell of the substation F, the ring contacts or the jack J2 andplug TP', to battery and ground through the alternate contact ot' theringing key RK2. The ringing key Rl@ upon actuation has its normalcontact 163 opened, opening the initial enegizing circuit ot' relay DSextending through thejupper Winding of the y as the ground Afrom thesleeve ot the jack J2 is now extended through the lower winding 01:' thesaid relay DS', the said relay is held energized when the ringing kkeyRK2 is actuated.

T he subscriber, in response to his call signal, removes hisreceiver'from the switch.- hook, and the closing 'of the switchliookcontacts permits the energizing ot' the super-` visory relay SR', thesaid currentiior energizing said supervisory relay SR being ted from themain exchange battery. The closing o'r' alternate contact 170 of thesupervisory relay SR' closes an energizing circuit tor the relay 161,traced from battery through the upper winding olf the said relay 161,conductor 171, alternate contact 17() of the ref lay Slt', conductors172 and 165, the sleeve of the plug TP', to ground at the sleeve ot thejack J2. The relay 161 upon energization closes its alternate contact166, es-

tablishing a locking circuit tor the said ref.

lay, traced from battery, tln'ough the winding ot the said relay. itsalternate contact 166, conductor 165, the sleeve ot the plug TP'. toground at the sleeve ot the jack J2. The closing o1 alternatevcontact176 ot the relay SR' also closes the holding circuit for the relay DS',traced from battery through the upper winding of the said relay.conductor 171, alternate contact `170 ci re lay SR', conductors 17 2 and165, the sleeve ot the trunk plug TP' to ground at the sleeve oit thejack J2. tact 166 ot Athe relay`161 brings about the BTS Y l 1,664,665

eiraoiaeneof the hcliifaig` Sign-sinn, which l'elayfSR establishesanenergizing circuit for the disconnect signalf'DSL from battery Y.through the lamp DSU, conductor 1'?" 5, al-

tel-nate contact 176 of relay 161, conductor 177,normaljconta`ct .1750of relayl SR', con-1l ductors 172,165, the sleeve of the plug TP to,ground-,attire sieeveof-the jack J?. Thevv clos-ing'fofnrmal contact170 of relay SR `also establishes an energizing circuit for the.disconnect relay ISR, traced' from battery through-the Winding of thesaid relay DR, conductor 175, alternate contact 176 ot lthe relay161,'conductor 177, normal contactlO, conductors V172 and 165, thesleeve of the trln'ilv plug TP to ground at the sleeve v'IlierelayDRn-pon; energizing opens its normal contactsY 180,181, opening thecontinuity` of the trunkcond-uctors, and should the subscriber at theprivate Vbranch exchangeF reca'l-h-theremoval of his receiver from the'"switchho'okl brings aboutithe enegization of thesu'pervisory recallrelay SE,

traced from battery through the lower Wind-v.

ing ofthe saidV relay SE, alternate contact 181 of relay'DR,`theringVcontacts kof the connected plugY TP andjackzJz, through the closedcontacts of the svvitchhook at thesta-` tion' F, back through the tipVcontacts of the connected plug'TP and jack J2, throughn alternatevcontact 180 of relay DR, to ground through the upper Winding of thesaid relay vSE..r The rela-y SE uponenergizationcrloses its alternatecontact1-82, which againlightsj thef line 'lamp LL, toground' atalternate contact 182` of relay SE, notifying the oper ator at theprivate branchy exchange trunk PC that the substation F. is recalling.The operatornovv actuate's her 'listening key LK2 to connect heroperators set'OZfto thet-runlr conductors,y andv to vextend-theconnection to the main exchangershe novv withdraws theV trunk plug TPfrom the jack J2,1-\vlii.ch

`Withdrfwval opens the loic-king circuit ofthe relay 161, which allowsthe said relay 'torestoreto normal. lThe closi-nnof normal Contact 160of the relay 161 again closes air energizing circuit for relayDS" overapath as previously described. Y' `Relay 161 uponV deenergization-ailsoopens the energizing` cir-V cuit ofthe relay DR atits alternate contact176:A The-relay DR *uponV 'deenergization' opens itsalternate`contacts'180 and 181, allowing the said supervisory recallrelay is readily SE to restore, and .the openingof its alternate contact182 etl'ace's the line LL. The operator new' again' ,inserts` the"Atrunk plug- TP into the jack J bringin'fb'` about the energization ofthe supervisoryre lay SR and the relay 161, as previouslyfjY` described.The closing ot normal contacts 180. and 181 of the relay DR now closesthcontinuity el the trunk conductors and ezfi tends the said privatebranch e'Xcl'i-ange sub1 station F to'fthe main' exchange, andtheoperation of the circuit from this pointon.`

scriptiori'.` I Should, the operator Wish to entend a apparent fromY theprevious del connection to amain` automatic exchange", f

she actuatesh'er listeningiley LK?, and' they closure of alternatecontact 185 lof the riiig u ing` key LK2 extends 'groundl to' contacts186 and 187L of theY Shun-t Springs ofthe @211;1iiig11 device CD. Theshunt springs 4186 I8l are closed, extending thegroundirorial# 'uternate Contact 185V to the listening key through thenovv closedcontacts`j186 and 187,;

overy conductor 188, througlfthe Winding" of the trunk cut-oli relay CORto batteryif The closing oi alternate contacts 189 and `190 of VtherelayV COR W connectsthe calling' device impulse springs overcondu'ctorsfjl"91` and 192, through alternate contacts 189 ing to themain automatic exchange'. After` 95. 190, directly to thetrunkconductors lead-fV th 'called-rorparty at 'the 'mais automaticexchange has been selected and'ain'svvers, the operation of'thevtrunkcircuit PClisth'e: same as previously described, and a further Vleudescription of its' operation lis notl 'deemed` i necessary.

Thetrunk PC', of coursegris 'arranged so that. the' Subscriber F @am dalhis Own an: nection. Connections can also'be extended to the branchexchange While the plug` isv in* Aa.jacln'ivithout ringingthe" connectedsubi scriber. In general, the circuit is'fcapable of use in establishingthe sjameconnectinsf as more fullyQeXplainged in''connection'k with" ctrunk circuit PC of Fig. Vl;

Referring; t. Fig. represents au.

r toinatic -Subj-station, Y an' individualf` Hilfe switch, 308 anautoinatic'selector switch, 3021'V kan automaticconnector switch, BOSthe'bariliH terminals' of( the connector switch, and B06 an automatic lineAswitch" or .anv aut-0inatiefA selector switch associatedfvvith theprivate'L branch ,exchange trunk and thefconduclzo tor's82l andAQleading- `frointlie cenne"etfn` switch Ycontacts 304 arejonn'ectedtythe" trunk circuity PG as isfwell underfstood;`V Of' 'l Course, any`number of selectors Ih'ayjbe in# serted inv the 'systemI according tostliesizey of the automatic exchange; c

In working out our invention vvehaveexil?y plol'ed pfferred'circuitarrangements all of which 'tend to make eficient 1opcrafting" system,butit is te be understood that va# nece-ece 9 rious changes andmodifications may readily be made without departing from the spirit andscope ot' our invention. Thereiormwe do not desire to be limited to theexact arrangement shown and described, but aim to cover all such changesand modifications as come within the spirit and scope of the appendedclaims.

'What welclaim as new and desire to secure by United States LettersPatent, is: l. A tele-phone system including a calling subscriber-sline, a called subscribers line, automatic switches and a trunk circuitprovided vwith a manual terminal for interconnecting said subscriberslines, automatic means in the trunk circuit tor clearing the same whenthe called subscriber replaces his receiver se that, a second call maybe eX- tended from said automatic switches to said trunk circuit'withoutoperating the call bell at the called substation, and means for saidtrunk circuit for denoting a recall by the called subscriber.

2. A telephone system includingy a calling; subscribers line, a calledsubscribers line, automatic switches and a trunk circuit provided with amanual terminal for interconnecting said subscribers lines, andautomatic disconnect means for said trunk circuit op erableby the calledsubscriber so that the trunk circuit is cleared betere the trunk cir-1cuit terminalis disconnected from the called subscribers line, therebypermitting the called subscriber to operatehis automatic dial to edect asecond connection or permit another subscriber to operate the automaticswitches and extend a call to said trunk circuit without signaling thecalled subscriber.

3. A telephone system includingq a calling subscribers line, a calledsubscribers line, automatic switches, and a trunk circuit provided witha manual terminal for interconnectinn` said subscribers line, andsubscribercontrolled means in said trunk. circuit for clearing the sameso that the called subscriber may actuate his calling device to effeet asecond connection or the operator may actuate her calling device to`effect a second connection prior to the time that the trunk circuitterminal is disconnected from the `called subscribers line.

4. A. telephone system including a trunk circuit provided with a manualterminal for connection to a called subscribers line, automatic switchesaccessible to said trunk circuit. an automatic calling device, and4operators means for operating said calling device to control saidautomatic switches while said trunk circuit is connected to saidsubscribers line, said means being operable whether the calledsubscriber has his receiver on or eti the switchook.

5. A telephone system including a trunk circuit `provided with a manualterminal tor connectiomto a subscribers line, automatic switchesaccessible to said trunk circuit, a

calling` device associated Awith said trunk circuit, means forconnecting said calling device to said trunk circuit to actuate saidautomatic switches to eilect a connection, and means tor said trunkcircuit operable to bridge a condenser across the trunk circuit ybetweenthe sets4 of impulses of the called number. f

(i. A telephone system including a-calling subscribers line, a calledsubscribers line, automatic switches and a trunk circuit4 pro vided witha manual terminal 'tor interconnecting said subscribers lines, a dialfor each subscribcrs substation, means in said trunk circuit forclearing thesame when a called subscriber replaces his receiver so thathe may again remove his receiver and operate the dial at the substationto operate the automaticswitches to eii'ect a second connection beforethe plug in the trunk circuit is disconnected trom the calledsubscribers line,

and automatic means for said trunk circuit for denoting a recall by thecalled subscriber.

7. Aitelcphonc system including a calling` subscribers line, aY calledsubscribers line, a trunk circuit provided with Va manual terminal forconnection to said called subscribers line automatic switches adaptedtobe connected to said trunk circuit, means for informing the operator` atthe trunk circuit that an automatic switch 4has been connected `to thesaidtrunk circuit, a signal Jfor said trunk circuit operable when saidtrunk' circuit is connected to a called subscribers line, a disconnectsignal7 automatic means for severingl the cuit, and subscribercontrolled means for operating said automatic means and said disconnectsignal..

strands ot the trunk cirl 8. A telephone system includinefa called lsubscribers line, a calling subscribers line terminating at an automatic"exchange, a trunk circuit having1 a manual terminal for connection to asubscribers line, automatic switches at said automatic exchange forconneet-ing said calling subscriber to said called subscriber via saidtrunk circuit. a discon nect relay, and means operable by one ot saidsubscribers when he signals for discon nection for operating` saiddisconnect relay for discrnuu-fctinghis line Jfrom the othei` ot saidsubscribers lines and for again eiieet inn' an operation ot said relayto connect the said subscribers line to the trunk circuit when theVsubscriber signals for a recall.

9. A telephone system including a calling: subscribers line and a calledsubscribers line, a private branch exchange having a trunk circuitprovided with a` manual terminal for connection with said calledsubscribers line, automatic switches adapted to connect said subscriberslines via said trunk lli) circuit, "a relay forsaid trunk circuit, asecond Vrelay for said trunk circuit, means controlled by said vcalledsubscriber for disconnecting his line `from the trunk conductor leading'to said kautomatic switches aindfor ybridging the battery at the-privatebranc'h exchange across his line, :whereby When he reinoveshisreceiver to institute a recall he energizesvthe said second` relay tocause the operation of said-first relay to again connect his line'to'the automatic exchange over the said trunkcondnctors.

w10( VA telephone system including a main excliange,"a.private branchexchange, auto-A matic switches at said mainexchange and a trunk circuithaving a manual terminal `at said private branchexchange forconnectiing'a subscriber at the said automatic exchange, a relay `forsaid trunk circuitk controlled by the subscriber at the private branchexchange and operable to connect 4either the battery at the privatebranch exchange' or the battery at the main exchange' across the saidsubscribersline.

l-l. A telephone"system'including'4 a calling subscrlbers vlineterminating at a main Nexchan e automatic switches at said -1nainexchange, a called subscribe1"s lineterminat- Ving at a private branchexchange, a Vtrunk circuit at said private branch exchangey providedWitha'inanua'l terminal for connection Vto'said called subscribers line,said auto matic switches and said trunkiv circuit for vinterconnectingthe said subscribers lines, a Y relay controlllnglthe connection of nsaid call `lngsubs'cribersV line to said called subscribers line, and `aSecond relay controlled vover said called `subscribers hne,1said secondrelay. being adapted When said called subscriber replaces his receiver,to operate Vsaid first krelay to l disconnect said subscribers lines,saidl relay upon` the snbsequent're- Inoval of said subscribers receiveroperable to again connect the subscribers lines.

12. A telephone system including a calling snbscribers lineuterminatingat a main exchange,;avcalled subscribers line terminating at a branchexchange, automatic switches at said main exchange and a trunk circuitat said branch `exchange provided with a inanual terminalu'or-interconnectingy the said subscribers lines, dialing means ior the`operator at said `trunk circuit, subscribers dialing means, .ln'eans1controlled by said calledjs'ubscriber for disconnecting his line fromthe trunk conductors leadingto' the said vautomatic 'switches,upon thereplacing of his` receiver upon itsswitchhook, means operable to againconnect his' line' to the said automatic exchange, means whereby thesaid' calledsubscribermay then dial to operatethe'said switchesat saidmain exchange and means whereby the `operator at the said trunkcircuitina'y'be informed of the recalll and operate her dialing` meanstoj/operate ythe said' automaticlswitc'hes at saidrmain exchange. l f

Signeclbyu's at Chicago,in theyc'ountyof Cook and State ofl'llinois,this4th day of March, 1925.",` y i l Y HIRAM D. CUR-BIER.

WILLIAMAG. SHELL.'

